Low-tension sparking plug



July 11, 1961 PRAS LOW-TENSION SPARKING PLUG Filed June. 18, 1957 www 2,992,352 LOW-TENSION SPARKING PLUG Lucien Pras, Billancourt, France, assignor to Regie Nationale des Usines Renault, Billancourt, France, a French government Works Filed .lune 13, 1957, Ser. No. 666,300 Claims priority, application France July '6, 1956 3 Claims. (Cl. 313-131) This invention relates to spark plugs and relates more particularly to improvements in low-tension ignition spark plugs operating by discharging a condenser.

It is known, in low-tension spark plugs adapted, by discharging a condenser, to ensure the ignition of the air-fuel mixture in internal combustion engines, to constitute the sparking element proper in the form of a pair of electrodes spaced about 0.1 to 0.3 millimeter apart, this gap being bridged by an insulator on the surface of which the sparks slip or slide.

The improvements forming the subject-matter of this invention relate to a spark plug of the type broadly set forth hereinabove which is characterized by a specific arrangement of its different component elements comprising the spark electrodes. This spark plug has the substantial advantage of ensuring, for instance in internal combustion engines, a useful Ilife much longer than that of any other low-tension spark plugs proposed heretofore.

This invention consists in providing low-tension spark plugs adapted `for use more particularly in internal combustion engines, wherein the metal electrodes between which the spark is caused to occur, are in the form of cylinders or prisms the respective shape and position of which are subordinate to the fact that the outer surfaces are generated by a common generatrix. The relative spacing of these electrodes is of constant, moderate thickness of the order of from 0.06 to 0.3 mm.; this intermediate space with a at or otherwise shaped base is occupied by an insulator and the spark will slip on the outer surface of this insulator when a suitable low-tension discharge is produced between the electrodes of the spark plug.

According to the specific embodiment of this invention the insulator, instead of consisting of a thin disc having the same thickness as the spark gap formed between the electrodes, is a cylindrical member formed with a shoulder having the same thickness as the aforesaid spark gap, this member being housed in a suitable cavity formed in one of the electrodes so that the shoulder occupies the spark gap to constitute the active surface on which the sparks are adapted to slip from one electrode to the other.

Two typical embodiments of spark plugs made in accor-dance with the teachings of this invention will now be described with reference to the attached drawings forming part of this specification and showing these embodiments in diagrammatical form. In the drawings:

FIGURE 1 is an elevational section showing a first embodiment, and

FIGURE 2 is a fragmentary axial section showing a modified embodiment.

Referring to FIG. l, the electrodes of the low-tension spark plug according to the invention are designated by the reference numerals 1 and 2 respectively. The electrode 1 consists of a washer of refractory metal such as tungsten or thoriated tungsten, and the other electrode 2 consists of a hollow cylinder also of refractory metal, the outer diameter of the cylinder corresponding to that of the washer 1. The bore of the cylindrical electrode 2 terminates at one end with a tapered portion or edge 3. The insulator consists of a washer 4, preferably but not necessarily of mica, having an outer diameter equal to States arent that of the electrodes 1 and 2. The body of the spark plug is designated by the reference numeral 5 and the terminal-forming screw rod by the reference numeral 6. This rod is formed with a mushroom-shaped head, as shown.

rThe component elements of the spark plug are assembled as follows:

The cylindrical electrode 2 is force fitted in the bore of the body 5 and the washer-shaped electrode 1 is threaded on the rod 6 until it engages the mushroomshaped head thereof, whereafter the insulating washer 4 is threaded in turn on the rod 6. If desired, the electrodeforrning washer 1 may be brazed on the mushroomshaped head of rod 6. Then the latter is positioned with its washers in the spark-plug body 5 so that the insulating washer 4 engages the outer end of the cylindrical electrode 2 near the tapered portion 3 thereof.

'Ihis electrode 2 is filled with boro-silicated glass 7 obtained by either heating a deposit of powdered glass as taught by the applicants U.S. patent application Ser. No. 632,048 of January 2, 1957, which is now U.S. Patent No. 2,940,221, granted June 14, 1960, for Improvements in or Relating to the Manufacture of Low-Tension Sparking Plugs for Internal Combustion Engines, or by compressing glass within the electrode placed in a jig or like mounting as taught by the applicants U.S. patent application Ser. No. 632,143 of January 2, 1957, which is now U.S. Patent No. 2,932,920, granted April 19, 1960, for Method of Manufacturing Low-Tension Sparking Plugs for Internal Combustion Engines, or by any other adequate method.

0f course, the glass or like insulating substance is introduced in the electrode 2 before engaging the latter in the body of the spark plug. The lower end of the electrode 2 filled with glass or like insulating substance is accurately Iground so that the glass and the flat end of the electrode are strictly flush and co-planar with each other.

The body 5 of the spark plug consists of a metal member insulated by a suitable porcelain or other insulator 8 and also by a substantially frusto-conical Bakelite or similar element 9 from the central steel tube 10 in which the current feeding rod 6 is threaded, as shown.

The electrodes 1 and 2 need not necessarily be of a straight cylindrical circular shape, as shown by way of example; thus, this straight section may differ in shape as consistent, for example, with the design of the combustion chamber, without departing from the spirit and scope of the invention. Besides, the electrodes may also have a prismatic form.

For the sake of economy, the electrodes may also consist of a thin tungsten crown or sleeve welded on a steel body, instead of being of solid refractory metal.

The spark-bridging insulator may consist of a substance other than mica. Thus, more particularly, it is possible to use insulating substances having a high dielectric constant the beneficial features of which have t already been set forth by the applicant in U.S. patent applicatiotn Ser. No. 651,264 of April 8, 1957, which is now U.S. Patent No. 2,926,275 granted February 23, =1960 for Slipping-Spark Ignition Sparking Plugs.

A permanent compression of the insulator between the two electrodes is obtained by providing on the portion of the rod 6 which emerges from the top of the tfrusto-conical insulating element 9 a plurality of spring washers 12 disposed by pair with opposed convexities, `as shown. These spring washers bear on the top end of the sparking plug and are loaded by a nut 11 screwed on the rod y6.

It 4will be noted that particularly beneficial results have been obtained by utilizing the following dimensions for some of the component elements of the sparking plug according to this invention:

Thickness of the electrode-forming washer 1: 0.1 to 3 mm.;

Width of the annular flat lower end of the cylindrical electrode 2 which contacts the insulator 4: 0.1 to l millimeter;

Angle formed between lthe generatrix of the tapered portion 3 and the annular flat lower end of the cylindrical electrode 2: 140 to 175;

Thickness of the insulating washer 4: 0.06 to 0.3 millimeters.

The insulator of constant, adequate thickness positioned between the electrodes is essentially a self-contained element shaped before being placed in position.

However, this shaping operation may be completed, if desired, after the assembling step, by grinding off any projecting chips or the like, or through another mach-ining operation. The insulating washer bears with one side on a metal surface and wit-h its other side on a surface consisting partly of the refractory metal and partly of glass.

The tapered portion `formed in the electrode 2 restricts the occurrence of sparks between the two electrodes to a depth consistent with the proper ignition of the air-fuel mixture in the combustion chamber.

The resilient clamping device illustrated, which comprises the spring washers of helical, tapered or partspherical form, is located in the cold region of the sparking plug and preferably externally thereof so that its properties are preserved.

As already stated hereinabove, the electrodes may be fabricated by welding a thin crown or sleeve of a refractory metal on a steel body, the thickness and width of the crown or sleeve being however suicient to have the volume of refractory metal available slightly greater than the volume of the space in which the spark is caused to occur.

Another typical embodiment of this invention is illustrated in FIG. 2 showing one end of a low-tension sparking plug having its electrodes purposely slightly spaced from each other.

In this modified embodiment, the insulator 21 disposed between the electrodes 22 and 23, instead of being a thin disc, consists of a cylindrical member sunk in a central cavity formed in the electrode 22 (corresponding to the electrode receiving the borosilicated glass lilling). This member 21 is lformed with a shoulder 24- occupying the intermediate space between the outer edges of the electrodes so as to constitute an active sparking surface.

The insulating member, whatever lits shape may be, consists of ceramic for example ceramic having a high dielectric constant, that is, higher than 70 where unity is the dielectric constant of a vacuum, according to the aforesaid U.S. Patent Serial No. 651,264 iiled April 8, 1957, for Slipping-Spark Ignition Sparking Plug of enameled ceramic. However, the enameling may be limited to the sparking zone only, between the electrodes.

In both embodiments of the invention the insulation 7 and the insulation 21 and more particularly shoulder 24 tit into an enlarged inner bore of the respective tubular electrodes 2, 22. It is readily apparent that the internal diameters of the bores of the tubular electrodes have a radius substantially greater than one half the transverse dimension or radius of the insulator washersV 4, 23 so that the insulators in the bores of the tubulai electrodes have a surface making intimate contact with the respective washers 4, 23 on at least a major area of a face surface of the washer 4 in the case of the embodiment shown in FIG. 1 and over the entire face surface of the washer 23 in the embodiment of FIG. 2

face of the insulator washers 4, 23 is in intimate contact with the insulation internally of the tubular electrodes.

The spring washers 12 form a system applying cornpression to the insulation washers so that in conjunction with the insulators that the respective washers bear on the ability or capacity of the washer to support a spark uniformly on its outer periphery is increased as well as reduction of erosion due to the spark.

What is claimed is:

1. In a low-tension spark plug having a tubular body member, a tubular first electrode disposed coaxial with said body member internally thereof with an end face extending axially outwardly of the body member, a disc second electrode corresponding in overall transverse dimensions wit-h said tubular electrode and corresponding in peripheral configuration with said tubular electrode, said disc electrode being disposed spaced axially from said tubular electrode and coaxial therewith, an insulator washer disposed between said electrodes having same transverse dimensions and peripheral conguration as the disc electrode at least in a space occupied by it between the two electrodes, an electrically conductive, elongated, axially displaceable member extending axially through said body member, tubular conductor, said insulator washer, and the disc electrode and having means defining a radially extending surface integral therewith at one end of said member overlying said disc electrode, an elastic system disposed externally of said body member and having members symmetrically disposed relative to the elongated conductive member to place the elongated member in tension thereby to place said disc electrode in compression and maintain said electrodes in intimate physical contact with said insulator, and the tubular electrode having an inner bore with an enlarged internal diameter adjacent said end face disposed axially outwa-rd of the body member, said internal diameter having a radius substantially greater than one half the transverse dimension of said insulator washer, an insulation composition in said inner bore of the tubular electrode disposed making intimate contact with said washer electrode on at least a major area of a face surface of said washer insulator corresponding to at least the inner marginal surface area of said face of said insulator washer.

2. In a low-tension spark plug having a tubular body member, a tubular first electrode disposed coaxial with said body member internally thereof with an end face extending axially outwardly of the body member, a disc second electrode corresponding in overall transverse dimensions with said tubular electrode and corresponding in peripheral configuration with said tubular electrode, said disc electrode being disposed spaced axially from said tubular electrode and coaxial therewith, an insulator washer disposed between said electrodes having same transverse dimensions and peripheral configuration as the disc electrode at least in a space occupied by it between the two electrodes, an electrically conductive, elongated, axially displaceable, member extending axially through said body member, tubular conductor, said insulator washer, and the disc electrode and having means deiining a radially extending surface integral therewith at one end of said member overlying said disc electrode, an elastic system disposed externally of said body member and having members symmetrically disposed relative to the elongated conductive member to place the elongated member in tension thereby to place said disc electrode in compression and maintain said electrodes in intimate physical contact with said insulator, and the tubular electrode having a conically spaced inner bore with its greatest internal diameter adjacent said end face thereof disposed axially outward of the body member, said enlarged diameter having a radius substantially lgreater than one half'the transverse dimension of said insulator, and an insulation composition in said inner bore of the tubular electrode having an end face surface substantially coplanar with said end face of the tubular electrode and disposed making intimate contact with said washer electrode on at least a major area of a face surface of said washer insulator corresponding to at least the inner marginal surface area of said face of said insulator Washer.

3. In a low-tension spark plu-g having a tubular body mem-ber, a tubular lirst electrode disposed coaxial with said body member internally thereof with an end face extending axially outwardly of the body member, a disc second electrode corresponding in overall transverse dimensions with said tubular electrode and corresponding in peripheral configuration with said tubular electrode, said disc electrode being disposed spaced axially from said tubular electrode and coaxial therewith, an insulator washer disposed between said electrodes having same transverse dimensions and peripheral configuration as the disc electrode at least in a space occupied by it between the two electrodes, an electrically conductive, elongated, axially displaceable, member extending axially through said body member, tubular conductor, said insulator washer, and the disc electrode and having means defining a radially extending surface integral therewith at one end of said member overlying said disc electrode, an elastic system disposed externally of said body member and having members symmetrically disposed relative to the elongated conductive member to place the elongated member in tension thereby to place said disc electrode in compression and maintain said electrodes in intimate physical contact with said insulator, and the tubular electrode having an inner bore with an enlarged A internal diameter adjacent said end Iface thereof disposed axially outward of the body member, said internal diameter having a radius substantially greater than one half the transverse dimension of said insulator, and an insulation composition in `said inner bore of Ithe tubular electrode disposed extending axially outwardly of said tubular elect-rode making intimate contact with said Washer electrode on the entire area of a face surface of said washer insulator, and the periphery of said insulator composition corresponding in coniigurati-on and substantially coplanar with the outer periphery of said tubular electrode.

References Cited in the tile of this patent UNITED STATES PATENTS 1,110,813 Noble Sept. 15, 1914 1,403,448 Ryder Jan. 10, 1922 2,135,297 Vila Nov. 1, 1938 2,170,243 Hornbach Aug. 22, 1939 2,260,399 Peters Oct. 218, 1941 2,357,602 Peters Sept. 5, 1944 2,415,138 Kasarjian Feb. 4, 1947 2,745,980 Smits May 15, 1956 2,786,158 Tognola Mar. 19, 1957 FOREIGN PATENTS 536,460 Great Britain May 15, 1941 631,386 Great Britain Nov. 2, 1949 

